Gravity and the Normal Force

          For most people, when we think of gravity, we think of things like, weight, and pulling down. Though gravity does pull down, there is a misconception that gravity is what causes our weight on whatever surface, which is wrong. We actually perceive weight through the normal force.
   
         The normal force is perpendicular to whatever surface an object is in contact with(if you’re in mid air there is no normal force). Gravity pulls down, normal force pushes up, hence a surface supporting our weight. Another point is Newton’s 3rd law: for every reaction(gravity), there must be an equal and opposite reaction(normal force). If  there was no normal force to support our weight, we would fall through the ground until we reached the Earth's center of mass.

      

            When solving for magnitude of the normal force, we use Newton's second law since it allows us to solve for a force. So, now you know that when there is a surface in contact with an object, the normal force is what supports that object. So what happens when someone is weightless? When there is an absence of gravity, why need a normal force to support you? In space, gravity is never completely absent(microgravity). You would have to be infinitely far from a mass in order for there to be absolutely no gravity. Astronauts in space feel weightless because they are in a constant free fall and there is no normal force. Remember I said in midair there is no normal force because there is no surface you’re in contact with? Weightlessness in space is that same concept. There is no ground to exert a normal force and the only force acting is gravity.
       
           So then why are the astronauts not literally falling toward the Earth? To successfully orbit the earth, you have to have the right velocity. If the velocity is too low, gravity will over power that velocity and pull you down to Earth. If the velocity is just right, there will be an equilibrium between the velocity and Earth’s gravity. The minimum orbit velocity for Earth is 17,000 mph.

          Another question one may find themselves asking about this concept is, can you only be in space to feel weightless? No! In order to feel weightless, there needs to be an absence of normal force, and you need to be in a free fall. At the fair, there are rides that bring you up really high then drop you. When you are in free fall, you are accelerating at -9.8 meters per second squared (acceleration of gravity). Whenever gravity is the only force acting upon you, you will feel weightless. Another example is in Apollo 13 the movie. The weightless space scenes were filmed in a free falling plane with only gravity pulling down. Once again, since gravity was the only force acting on them, they experienced weightlessness.

Newton and Infinity War

So in superhero movies, it is normal that you see superhuman strength that disregards Newton's laws. But because of this being a physics class, we will be picky with our laws and how they are portrayed. 

Newton’s first law states that an object that is at rest, will want to stay at rest, and an object in motion will want to stay in motion and stay in the same direction and have the same speed(or not) until acted on by an external force. In this weeks movie, there is a scene where Hulk plummets into the atmosphere and crashes into Dr. Strange's house, and goes through his stairs, and eventually stops. The first law is shown in this scene when he digs into the stairs and eventually stopped by the ground. The only reason Hulk stopped was because the force of the ground against his fast moving body. If there would have been no ground to crash into, Hulk would have kept on moving, because the first law says that an object in motion, wants to stay in motion in the same direction and speed. 

Newton’s second law states that when a force is acted upon an object, there WILL be an acceleration(even if you can’t see it) and it will be inversely proportional to the object’s mass. There was a scene in the movie where Thor had to get these artificial rings around a dead neutron star moving so he could get a new axe. So what Thor did, was started swinging/accelerating the raccoon(he was at rest previously) so fast, that his interia (need to keep moving that fast) and energy in his momentum transferred to the rings. This would not be feasible because I know those rings weigh A LOT, a huge number, and that raccoon probably weighs only 15lbs. The point is, Thor acting on the raccoon who was at rest, resulted in an acceleration due to force, but how the scene went down(the rings started spinning) is not feasible. 

Newton’s third law says that for every reaction, there is an equal and opposite reaction. In Infinity War, the battle was for these stones that ruled the universe. One of the characters, Vision, has one of these stones, the mind stone, ingrained in his forehead, and Thanos is trying to steal it. So Thanos sends his allies to try and get this stone. In the scene, Vision was fighting a villain named Proxima Night. Proxima night has this gun stick thing that shoots out some sort of energy bullet(that is how it was portrayed). In this scene, Proxima Night is trying to take down Vision with her gun stick. Each time she shoots it, I noticed there is no recoil. There is no equal and opposite reaction for the amerture shooting out the gun stick. This is wrong because when Proxima Night missed Vision, it would break the object it hits, which concludes that there is a lot of energy needed to get the bullet moving that fast, and there should be recoil.

Rating: PGP-13

NASA's Blow Up an Asteroid Plan(More Studying to Conduct)

So, scarily and unfortunately, there are not too many plans NASA has
in the case of a NEO hitting the earth. I did happen to find a small
article on NASA’s website about possibly blowing up an asteroid
though, sort of like in the movie Armageddon. In the movie, the plan
they had in real life wouldn’t work. The asteroid was just too close,
moving too fast, and the machinery and tactics they were using were
just too risky. There would be a small chance of a plan like this
working. In the movie they even said they had never seen metal on
the asteroid like that before. So there was no telling what crazy
properties it could have had. 

In the abstract plan I found, it presents the idea of fragmenting an
asteroid using hyper velocity kinetic impactor with a subsurface
nuclear explosion in place. The article states that this could work if
the asteroid fragments as needed. If we were able to blow off parts of
the asteroid, there would be a better chance of our planet surviving
because the asteroid wouldn't have as much mass as before(and could
maybe slow it down). What scares me about this though, is launching
a nuclear bomb into space using huge amounts of rocket fuel. If the
rocket ship were to blow up in our atmosphere with a nuclear bomb in
it, the consequences could be very bad. 

Another very important part of this plan, is that we blow the asteroid up while it is 10 years out, not a few hundred miles from earth. Not only would this give us more time to blow up the asteroid, but if the asteroid is blown up and the fragments speeds escape the asteroids escape velocity, the likelihood of them hitting earth is low.

We have to remember that this plan is very far out. This is a phase one
study, or idea. There is much more studying and investigating to be
done. Phase two will seek out IDC (Integrated Design Center), and
NASA’s Goddard Space Center for more studying on this topic.
They will be looking to examine the technical feasibility, and the
overall effectiveness of this plan. 

In the meantime, I hope a NEO doesn’t hit the earth in my lifetime.
If so, I will gladly but uneasily watch as it plummets into our
atmosphere to kill us all. At the same time though, if a NEO is on its
way, I hope NASA comes up with more plans to stop it. 

Eraser

This movie is a compilation of rail gun scenes, and every single scene is RP(retch physics). Whether a thug or buff Arnold is shooting the rail gun, there is first of all, no recoil whatsoever. Realistically, the recoil of a rail gun should blow off the top half of someone's body. Wouldn’t that be a great scene? On the other hand, when someone is shot by the rail gun, they are simply blown off their feet and hit the ground a few feet behind them. The conservation of momentum says that the momentum of the bullet should transfer to the target. So I did the math to see how much momentum the target man should have when hit by the bullet and this is what I found:





The target man should start moving at 1,113,514 meters per second when hit by the bullet. I don’t know exactly how much, but it takes an enormous amount of energy to get a 63 kilogram mass moving as 1,113,514 meters per second, especially all caused by a tiny little .26 gram bullet. Realistically, the target man should literally blow up so the energy of 1,113,514 meters per second has somewhere to go, other than getting the target man moving 1,113,514 meters per second which would be very, very hard. Only if the physics of the rail gun were real in this movie, because boy would that be a good movie.

Mission Impossible 3

In Mission Impossible 3 I was able to pick out two scenes I think I can analyze. The first one I noticed was in the shootout at the abandoned warehouse. Tom Cruise used his last bullet to shoot a bad guy and totally blew him out the window. Is this possible? The bullet was portrayed as having a massive amount of kinetic energy. I have no idea what kind of gun Tom Cruise was using so I will assume it was an AK gun. Using the internet, I found that the bullet of an AK 47 travels at about 715 meters per second and weighs about 1.5 grams. The diameter of the bullet is about 8mm. Considering how small the surface area of the bullet is compared to the chest of the enemy, the bullet should've gone through him and made him drop to the ground. The enemy could have been thrown out the window if he was hit with something with a larger surface area, such as a bowling ball(especially going at the speed of an AK 47 round). There was also an affect where the enemy was lifted off the ground because of Tom Cruise's bullet. I can’t explain this. Just by watching this scene I know it is not accurate from a physics perspective. 

Another crazy scene in Mission Impossible 3, was when Tom Cruise ran a mile in 1 minute and
50 seconds. This took place in Shanghai. I rewatched the scene on Youtube and noted how long
he was running. After converting 1 minute and 50 seconds into hours(.03056 hours), I used
distance/time=speed to find his speed which came up at about 32mph(51 kilometers per hour).
This is faster than Usain Bolt, who runs at about 28mph. I highly doubt that Tom Cruise has
more talent than Usain Bolt. I could be wrong, but I am pretty set on it! 

Tom Cruise is without a doubt, extremely brave. The only way to retrieve the rabbit's foot was to
swing to the neighboring building, hundreds of feet tall. Since we don’t know the exact numbers
for relevant quantities, I will estimate. First, we need to know Toms potential energy, so we can t
hen calculate his kinetic energy when he jumps. He weighs 150lbs, or about 67 kilograms. Next
we need to know how far the buildings are apart, which I estimate are 200 feet(61 meters). The
length of the swinging cable, which has to be as long as the width between the two buildings, I
will also estimate is about 205 feet(62 meters). When Tom Cruise jumps off the building, he
should convert most of his potential energy into kinetic. Before the cable catches up with him,
he is free falling. One the cable does catch him, I think he loses a lot of the kinetic energy he had
before, hence slowing down his swing to the next building. Also, you have to acknowledge air
resistance. Because of this, I think that Tom wouldn’t have had enough kinetic energy to make
this swing up. 

MOVIE RATING: PGP-13